In principle, incineration grates of the kind referred to above are well-known and are normally used with two or more sections mutually overlapping, the uppermost section functioning as an infeed grate apportioning the fuel into the incinerating plant from a fuel shaft above the upper part of the grate, whilst the function of combustion per se is served by the lower section or sections, the lowermost section also discharging the solid products of combustion, such as ashes and slags, to suitable removal devices.
In a grate of this kind disclosed in U.S. Pat. No. 4,471,704 and having two sections, adjacent grate beams are reciprocated longitudinally in opposite phase, and the stepped grate surface is formed by a number of grate elements placed edge-to-edge.
In another grate of the kind referred to, disclosed in U.S. Pat. No. 4,494,469, every other grate beam is reciprocable longitudinally, while the remaining grate beams are stationary. In this grate, the grate surface is formed by a number of grate blocks composed of grate rods, each block comprising two steps of the stepped surface.
U.S. Pat. No. 2,240,590 describes a fluid cooled grate beam comprising two longitudinally extending ducts for the cooling medium provided immediately below the grate surface of each grate beam and in heat transmitting contact with said surface and the lateral surfaces of the grate beam, as well as connecting points at one end of the grate beam for the flow of cooling medium towards and away from said ducts. However, thee grate beams are not placed sealingly close to each other along the lateral surfaces. On the contrary, the grate beams are provided with primary air openings along the lateral surfaces. This will result in a tendency to move material on the grate in between the grate beams which will lead to increased wear on the lateral surfaces of the grate beams.
FR-A-739,654 describes another fluid cooled grate beam comprising flat lateral surfaces but these surfaces are placed with spaces between them.
In incinerating plants for waste material, especially the infeed grate, i.e. the uppermost grate section in the plant, is subject to extremely inhomogeneous heat influences; this is due to its function and position in the plant as well as variations in the calorific value of the waste material being fed in by this grate, because the processes taking place on the infeed grate comprise both a drying of the waste material and an initial gasification and ignition of the latter, and the manner, in which all this proceeds and hence the heating of the grate, depends to a high degree of the (net) calorific value of the waste material, i.e. especially its moisture content.
In previously known incineration grates, such as those disclosed in the above-mentioned US patent specifications, these conditions have made it difficult to achieve an effective seal between the adjacent, relatively reciprocable grate beams, more particularly between their lateral surfaces; this is caused by the temperature differences along the grate beams creating differences in their degrees of thermal expansion. An insufficient seal between adjacent lateral surfaces partly results in a greater quantity of ashes and uncombusted waste falling through the grate, this obviously being highly undesirable in consideration of the desire to achieve a sterilization and combustion of the waste material, partly an unintended distribution of the primary air, passing in an uncontrolled fashion up through the gaps between adjacent lateral surfaces.
In order to achieve a better sealing function, incineration grates of the kind referred to initially normally comprise facilities for pressing the grate beams in each section together in the lateral direction, this also making it possible to accommodate attrition on the lateral surfaces of the grate beams. This attrition, being--of course--due to the relative movements of the grate beams, will, because of their material properties, be a minimum at a relatively low temperature.